In a circular knitting machine for the production of socks or knitted articles with argyle intarsia pattern obtained by a reciprocating motion - like the machine described in Italian Pat. No. 997,212 --it is necessary to select - before every yarn-feeding station and in both directions of motion - those needles which are going to knit with the yarn fed at that particular station. This selection is mechanically achieved by means of peg drums which act upon the butts of the selection jacks according to certain programmable sequences; this action is performed by dual fork-like selection levers superimposed to form a pack.
As it is known, the patterns obtainable by this method have, in the width direction, a maximum number of needles equal to the number of butts of the selection jacks which can be arranged diagonally (or, in the case of a symmetrical pattern, which can be arranged according to a double "V"-shaped diagonal) and have, in the length direction, a maximum number of courses equal to the number of rows of pegs available on the circumference of each pattern drum.
These limits in the possible patterns achievable could be overcome by adopting electronic programmers.
Nevertheless, direct control on this type of selection fork levers by means of electromagnetic actuators cannot be easily carried out either because of the necessary, considerable forces and high response speeds (which cannot be attained owing to the limited space available) or because the diagonal of the selecting butts should be wider than the levers themselves, in order to allow their up and down movement in the empty space between one diagonal and the other. It would be necessary, therefore, to increase the number of butts, make the cylinder higher and adopt other expedients with all the ensuring drawbacks.
It is possible to divide each pack of double levers into two packs of single levers, but this requires a number of packs of levers (and thus of electromagnetic actuators) twice as much as the number of feeds, with consequent big problems as for the space available around the cylinder and higher cost.